An optical pickup device for recording or reproducing information on or from an optical information recording medium such as DVD (Digital Versatile Disk) is provided with a lens for focusing light emitted from a light source on the optical information recording medium. This lens is opposed to the optical information recording medium in recording and reproduction and provided movably in a direction orthogonal to an information recording surface of the optical information recording medium and in a horizontal direction for the purposes of focus control and tracking control.
Recently, in order to realize high density recording, optical pickup devices using a laser beam of a short wavelength or a lens having a large number of apertures (NA) for recording and reproducing information have been proposed. The size of a recording mark of an optical information recording medium is proportional to the size of an optical spot, and it is possible to downsize the recording mark by downsizing the optical spot, thereby achieving improvement in recording density. When the laser beam wavelength is represented by λ, the optical spot size is decided by λ/NA. Namely, it is possible to improve the recording density of an optical pickup device by using the short wavelength laser beam and/or by using the lens having a large NA. For example, in the case of BD (Blu-ray Disk) developed as a large capacity optical information recording medium, it is possible to record information up to 27 GB on one side by using an optical pickup device using a blue-violet laser beam having a wavelength of 405 nm and an object lens having an NA of 0.85.
However, since a focal distance becomes shorter when the lens having large NA is used, a distance (hereinafter sometimes referred to as operation distance of lens) of the closest approach of the lens to a surface of the optical information recording medium is reduced. For instance, in one example of optical pickup device for BD, the focal distance is about 0.32 mm, and the lens operation distance is about 0.31 mm, which are remarkably short. As described above, due to the recent tendency of reducing the operation distance of the lens for the realization of high density recording, damages due to a contact between the lens and the optical information recording medium during operation of focus control and tracking control, for example, can easily be caused. Since the highest rotation speed of the optical information recording medium is about 150 km/h at its outer rim during recording and reproducing, at least one of the lens and the optical information recording medium is damaged when they contact with each other to make it impossible to record and reproduce information.
In order to solve the above problem, the optical pickup device has heretofore been provided with means for protecting the lens and the optical information recording medium from damages. For example, there has been proposed an optical pickup device provided with a protection member which is disposed on a surface opposed to an optical information recording medium of a component part retaining a lens, such as a lens barrel, and projected closer to the optical information recording medium than the lens is. As such protection member, a cushioning material made from a lamb felt (see Reference 1, for example), a projecting part made from a plastic which is more flexible than an optical information recording medium (see Reference 2, for example), a protector made from a silicon rubber (see Reference 3, for example), a protection lubrication film made from a non-crystalline carbon film and the like (see Reference 4, for example), a resin film produced by using a fluorine resin and the like as a base (see Reference 5, for example), and the like have been proposed.
[Reference 1] JP-5-144041
[Reference 2] JP-2-54433
[Reference 3] JP-11-312322
[Reference 4] JP-2001-297478
[Reference 5] JP-2003-272206
It is necessary for the protection member to reliably prevent the contact between the lens and the optical information recording medium as well as to avoid from damaging the information recording surface of the optical information recording medium when the protection member contacts the optical information recording medium. Therefore, the protection member is required to have an appropriate hardness for realizing a low friction property, a cushioning property (elasticity) for cushioning an impact of contact, and friction resistance.
However, as described in the foregoing, since recording and reproduction are performed in a state where the lens and the optical information recording medium are considerably close to each other in the case of the optical information recording medium of high recording density, an impact caused by a contact therebetween is great, and it has been difficult to protect both of the lens and the optical information recording medium with the use of conventional protection members.